As is well known, a hypodermic syringe is used to inject substances into human and animal bodies. A typical hypodermic syringe comprises a barrel adapted to contain the substance to be injected, a hypodermic needle coupled to the barrel and means, such as a plunger, for forcing the substance from the barrel through the needle.
Hypodermic syringes are typically disposable and are discarded after use. One problem presented by the disposal of the syringes is in shielding the sharp end of the needle so that those handling it will not be stuck. This is particularly important because, following the injection, the needle may be contaminated and spread disease, such as hepatitis.
Typically, a hypodermic syringe is supplied with a tubular shield which is slipped over the needle from the pointed end and releasably retained on the syringe. One way to shield the needle following its use is to replace the tubular shield. Unfortunately, the passage into the shield is of small diameter and the shield must be inserted over the sharp end of the needle. Consequently, there is a substantial risk to the person attempting to do this, particularly if the reshielding is attempted during emergency periods or other times of high stress.
Other methods of needle shielding are known and are described, for example, in Bastien U.S. Pat. No. 2,571,653, Leeson et al U.S. Pat. No. 3,890,971 and Wulff U.S. Pat. No. 3,780,734. However, each of these devices suffers from various drawbacks. For example, the Bastien guarded syringe does not positively retain the guard in position, and the devices shown in the Leeson and Wulff patents are quite complex with the latter device being particularly adapted for animal usage.